Conventionally, in a vehicle air conditioner provided with a heat pump cycle, when an outdoor heat exchanger of the heat pump cycle is frosted, the heat pump cycle is switched to a cooler cycle, thereby defrosting the outdoor heat exchanger.
JP-A-2002-174474 describes regarding a vehicle air conditioner that is provided with a heat pump cycle and a heater core. The heater core heats air to be blown into a vehicle compartment by using engine coolant as a heat source. In the vehicle air conditioner, in a case where an outdoor heat exchanger of the heat pump cycle is frosted, if the temperature of engine coolant is higher than a predetermined temperature, the heat pump cycle is switched to a cooler cycle, thereby defrosting the outdoor heat exchanger.
However, in the vehicle air conditioner, when the heat pump cycle is switched to the cooler cycle so that the defrosting of the outdoor heat exchanger of the heat pump cycle is performed, if the defrosting time is long, a heating feeling given to a passenger in the vehicle compartment is deteriorated.
Furthermore, in the vehicle air conditioner described in JP-A-2002-174474, when an engine operation is not necessary as a driving source of a vehicle traveling, such as in a case of an idling-stop vehicle or a hybrid car, it is difficult to obtain a sufficient heating feeling in the defrosting operation.
Thus, in the vehicle air conditioner, when the engine is stopped at a low temperature of the engine coolant, the defrosting can not be performed during the engine stop. Alternatively, when the heating operation using the heat pump cycle is switched to the defrosting operation using the cooler cycle, a heat source necessary for the heating operation is insufficient, and thereby the temperature of air to be blown into the vehicle compartment is decreased. Therefore, the heating feeling given to a passenger in the vehicle compartment is deteriorated.